Could the wind blowing when a train moves used to generate power; with a fan-like contraption?

I was thinking of adding an aerodynamic design on top of a train with a fan-like that will turn because of the wind and generate electricity for alternative energy source solutions; to use it somewhere else perhaps or even on the train itself. I was thinking that perhaps the fan would be in a contraption that resembles a slide with an opening on the lower side and the wind would pass through there to spin the fan while the metal casing would let the wind slide without generating a lot of resistance. Granted my physics are skethcy at best but I was wondering if something like this could be taken advantage of or the net worth would be nill, negative, or negligent....